Stationary radiographic imaging equipment are employed in medical facilities (e.g., in a radiological department) to capture medical x-ray images on x-ray detector. Mobile carts can include an x-ray source used to capture (e.g., digital) x-ray images on x-ray detector. Such medical x-ray images can be captured using various techniques such as computed radiography (CR) and digital radiography (DR) in radiographic detectors.
A related art digital radiography (DR) imaging panel acquires image data from a scintillating medium using an array of individual sensors, arranged in a row-by-column matrix, in which each sensor provides a single pixel of image data. Each pixel generally includes a photosensor and a switching element that can be arranged in a co-planar or a vertically integrated manner, as is generally known in the art. In these imaging devices, hydrogenated amorphous silicon (a-Si:H) is commonly used to form the photodiode and the thin-film transistor switch needed for each pixel. In one known imaging arrangement, a frontplane has an array of photosensitive elements, and a backplane has an array of thin-film transistor (TFT) switches.
As a result of the non-single crystalline structure of amorphous silicon, a large density of defect states exists within the photosensor. These defect states trap electrons and holes and release them with a time constant determined mainly by the energy level of the defect state, which is in some cases much longer than an imaging frame time. Generally, only trapped electrons of the photosensors are described herein, but it should be understood that holes can be trapped in a like manner and the same mechanisms apply to holes. Therefore, whenever the electric field within the photosensor/photodiode is perturbed either by electrons generated by light from an x-ray exposure, by the bias voltage being varied, or the like, trapped electrons within the photosensor are redistributed among these defect states, generating a detrapping current with a long time constant at the photosensor terminals.
Various U.S. patents address problems of large density of defect states of amorphous semiconductor materials (e.g., a-Si) and disclose various methods of operating DR detectors to reduce artifacts produced thereby. See for example, U.S. Pat. No. 5,920,070 (Petrick et al.) or U.S. Pat. No. 7,593,508 (Tsuchiya).
However, there is a need for improvements in the consistency and/or quality of medical x-ray images, particularly when obtained by an x-ray apparatus designed to operate with a-Si DR x-ray detectors.